Diffraction and diffraction gratingsEdexcel A-Level Physics: Flashcards

What these 14 flashcards ask

Define diffraction.
When is diffraction most pronounced?
State Huygens' construction.
State the grating equation.
How do you find d from lines per millimetre?
How is the highest order found?
Why is the central maximum of white light white?
Which colour is diffracted most by a grating?
Why do higher-order spectra overlap?
What happens to the maxima if the wavelength is shorter?
In the grating practical, why measure across both sides of the centre?
How is θ found in the grating practical?
What graph can be plotted to find the wavelength with a grating?
State a laser safety precaution.

Exam questions on Diffraction and diffraction gratings

In a ripple tank, a vibrating dipper produces plane water waves of wavelength 1.5 cm that travel towards two barriers with an adjustable gap between them. The speed of the waves in the tank is constant, and the frequency of the dipper can be changed.
Use Huygens' construction to explain why the waves spread into the region behind the edges of the barriers.2 marks
A student shines a red laser of wavelength 633 nm at normal incidence onto a diffraction grating with 600 lines per millimetre. A series of bright spots is seen on a distant screen, either side of a central bright spot.
Calculate the angle between the central maximum and the first-order maximum.2 marks
In a core practical, a student determines the wavelength of light from a laser using a diffraction grating with 300 lines per millimetre. The grating is held perpendicular to the beam and the screen is 1.00 m from it. The student measures the distance between the two second-order maxima, one on each side of the central maximum, as 0.850 m.
Calculate the wavelength of the laser light.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).